The present invention relates to a light modulator device with a spatial light modulator, a structured polariser means, a controllable polarisation means and a light wave multiplexing means. The spatial light modulator comprises discretely addressable modulator cells. Two modulator cells each are combined to form a modulation element. The modulator cells modulate light waves which are capable of generating interference of a propagating light wave field with holographic information in a spatially structured way such that a specifiable spatial distribution of object light points of a three-dimensional scene is holographically reconstructed. The modulator cells of each modulation element are arranged adjacently regarding the direction of propagation of the light wave field. The light which is modulated by adjacently arranged modulator cells is given different polarisation states by the structured polariser means. For this, a modulator cell or each modulator cell can preferably be assigned with a region on the structured polariser means. The structured polariser means could for example be designed such that it has regions with different polarisation properties. Such a region could have a dimension that corresponds substantially with the cross-sectional area of the modulator cell or column or line of modulator cells which is assigned to that region. The light wave multiplexing means is disposed and designed such that the different light wave portions—after having been modulated by the modulator cells and having different polarisation states—are combined on its exit side to form a modulated light wave multiplex such that the modulated light wave multiplex leaves the light wave multiplexing means substantially though a common point and substantially in the same direction of propagation.
A light modulator device of the aforementioned type is known for example from the international patent application no. WO 2010/149588 A1. The light modulator device described there comprises light wave multiplexing means which are disposed and designed such that the different light wave portions—after having been modulated by the modulator cells and having different polarization states—are combined on its exit side to form a modulated light wave multiplex such that the modulated light wave multiplex leaves the light wave multiplexing means substantially though a common point and substantially in the same direction of propagation. Thanks to this, it is possible to preferably use spatial light modulators which serve for example to modulate the phase of the light which passes through one modulator cell in a specifiable different way than the phase of the light which passes through another, adjacent modulator cell. If the light which passes through the adjacent modulator cells can be spatially superimposed and combined to form a light wave multiplex which propagates substantially in the same direction of propagation, then the light wave multiplex which comprises the light which has passed through the adjacent modulator cells can serve as a complex hologram value with which a three-dimensional scene can be holographically reconstructed. In the light modulator device according to WO 2010/149588 A1, in particular for a holographic display with single-parallax encoding (1d), the modulator cells of adjacent lines or columns of a spatial light modulator are combined such that corresponding lines of modulation elements or columns of modulation elements are formed. The resolution of the three-dimensional scene which can be achieved with such a display can be chosen freely. In the direction which is perpendicular to the latter, that is in the sweet spot direction, the scene resolution is limited by the number of modulator cells of the spatial light modulator (SLM) in that direction. As a result, however, the resolution of the three-dimensional scene which is to be displayed is lower in the direction which is perpendicular to the respective line or column of modulation elements. Without prejudice to the generality of the invention, it is assumed hereinafter that a vertical parallax only encoding is used. Then, the scene resolution can be chosen freely in the vertical direction, whereas it is limited by the number of pixel columns in the horizontal direction. Since the inventive light modulator device described hereafter can form a continuation of the light modulator device described in document WO 2010/149588 A1, and since reference is made hereinafter to the light modulator device described in document WO 10 2010/149588 A1, this document is fully incorporated herein by reference.
If the holographic display comprises a spatial light modulator whose modulator cells can modulate the phase of the light which interacts with the modulator cells and a light wave multiplexing means with the function of combining light which passes through two modulator cells to form a complex-valued light wave multiplex, then the scene resolution is halved compared with the number of columns of modulation elements.
It is therefore the object of the present invention to provide and to advance a light modulator device of the aforementioned type such to overcome the aforementioned problems. It shall in particular be avoided that the resolution of the reconstructed three-dimensional scene is reduced as light of adjacent modulator cells is combined.
The object is solved according to this invention through the teachings of claim 1. Further preferred embodiments and continuations of the present invention are defined in the dependent claims.
According to this invention, the light modulator device of the aforementioned type is characterised in that in a first operational situation of the controllable polarisation means light wave portions of two adjacent modulator cells are combined by the light wave multiplexing means, whereas in a second operational situation of the controllable polarisation means light wave portions of two other adjacent modulator cells are combined by the light wave multiplexing means.
According to this invention, it has first been found that the scene resolution can in particular be prevented from being halved when two holograms or two three-dimensional scenes are shown sequentially in one direction, in particular in the incoherent direction, by using a light wave multiplexing means which would work in a polarisation-sensitive mode. This can be achieved by switching the controllable polarisation means, whereby the polarisation of the light is changed before it passes through the light wave multiplexing means, so that the light wave portions of two adjacent modulator cells are combined by the light wave multiplexing means in the first operational situation of the controllable polarisation means, and that the light wave portions of two other adjacent modulator cells are combined by the light wave multiplexing means in the second operational situation of the controllable polarisation means. Here, the two other adjacent modulator cells can be offset by one modulator cell from the two adjacent modulator cells. Thanks to this measure, a first and a second three-dimensional scene are reconstructed on the exit side of the light wave multiplexing means which are usually offset by one column or line of modulator cells. To give an example, the modulator cells of columns 1 and 2, the modulator cells of columns 3 and 4, and so forth, are each combined to form a complex value for the three-dimensional scene which is shown first. Then, the modulator cells of columns 2 and 3, the modulator cells of columns 4 and 5, and so forth, are each combined to form a complex light wave multiplex for the three-dimensional scene which is shown thereafter.
This way, the light modulator device according to this invention preferably allows the resultant scene resolution to be doubled compared with the light modulator device known from document WO 2010/149588 A1.